In certain technical equipment such as, for example, scattered-light smoke detectors, light is selectively introduced into a useful light region, for example a scattered light region, and any reflections there may be are detected by means of one or more optical detectors such as, for example, photodiodes and the like. In scattered-light smoke detectors, almost monochromatic light or infrared radiation of a laser or light-emitting diode generally propagates in a straight line from the light source into the useful light region. When scattered there by any smoke or similar particle there may be, a lesser amount of this scattered (reflected, as the case may be) light strikes the optical detectors arranged around the useful light region, whereby a signal is produced in same. Depending on the application, different signal processing methods are thereby used; should certain conditions be fulfilled, this type of scattered-light smoke detector can emit a warning signal or the like.
Of great importance in such applications is for structural measures to ensure that apart from the scattered light, which is actually scattered and/or reflected on the particles to be detected within the useful light region, as little stray light as possible reaches the optical detectors. Stray light is light which is for example reflected by the inner walls, etc. of the scattered-light smoke detector. When too much stray light strikes the optical detectors, the optical detectors produce too high of a background signal such that the stray light barely stands out from the background signal and is therefore difficult or impossible to detect. Particularly in the case of highly sensitive scattered-light smoke detectors, it becomes necessary to greatly amplify the scattered-light signals, which would lead to overmodulation of the amplifier at high background signals.
Light traps are known for the purpose of attenuating or absorbing unwanted light. For example, printed publication DE 10 2005 045 280 B3 discloses an optical distance sensor having such a light trap, whereby the light trap is arranged in the direct proximity of the light source in order to absorb the scattered light which propagates directly from the light source in a different direction than the nominal direction of the beam to be emitted. This conventional light trap is of relatively complicated structure, whereby incoming beams of light are reflected by the light trap such that they die out and are no longer routed out of the light trap. To this end, the conventional light trap provides for scored surfaces or folding within the light trap.
The light trap known from DE 10 2005 045 280 B3 thus has a relatively complicated structure for the purpose of effectively absorbing impinging light. The conventional light trap is moreover arranged to the side of a photo-optical receiver and thereby only serves to attenuate light reflected onto said receiver; i.e. on its surface. Therefore, in the case of an arrangement as found in a scattered-light smoke detector or the like and in which the beam of light (beam) emitted by the light source is not conducted directly onto a receiver element, this conventional light trap is not suited to sufficiently absorbing the directly impinging and relatively strong beam of light and thus preventing it from reflecting back into the useful light region.